Brushless d.c. motor using magneto resistor sensing means

ABSTRACT

A brushless d.c. motor having a diametrically magnetized permanent magnet rotor and a plurality of stator windings disposed around the inner periphery of the motor frame, employs magneto resistors placed intermediate adjacent windings to trigger commutating switches that control energization of the individual stator windings. All stator windings are wound to attract the same selected magnetic pole of the rotor. The rise in resistance of a magneto resistor when subjected to flux from the selected magnetic pole is used to close the switch controlling the following stator winding in the desired sequence. The switch also produces a disabling signal that triggers a silicon controlled rectifier in the preceding switch so as to open this switch. The magneto resistor controlling the disabled switch is disposed diametrically opposite the energized stator winding so that when the flux from the non-selected rotor pole intercepts this resistor, the associated switch remains clamped in the open condition.

@ttes Patent 11 1 [111 3,71%,75

Holland et al. 1 March 15, 1973 [54] BRUSHLESS DC. MOTOR USING [57]ABSTRACT MAGNETO RESISTOR SENSING MEANS Inventors: Eugene E. Holland,Charlottesville; Rex 0. Jones, Ill, Burgess, both of Va.

[73] Assignee: Sperry Rand Corporation, New

York,N.Y.

22 Filed: Jan.26,1972

[21] Appl. No.: 220,932

Primary Examiner-G. R. Simmons Attorney-Howard P. Terry A brushless d.c.motor having a diametrically magnetized permanent magnet rotor and aplurality of stator windings disposed around the inner periphery of themotor frame, employs magneto resistors placed intermediate adjacentwindings to trigger commutating switches that control energization ofthe individual stator windings. All stator windings are wound to attractthe same selected magnetic pole of the rotor. The rise in resistance ofa magneto resistor when subjected to flux from the selected magneticpole is used to close the switch controlling the following statorwinding in the desired sequence. The switch also produces a disablingsignal that triggers a silicon controlled rectifier in the precedingswitch so as to open this switch. The magneto resistor controlling thedisabled switch is disposed diametrically opposite the energized statorwinding so that when the flux from the non-selected rotor poleintercepts this resistor, the

associated switch remains clamped in the open condition.

8 Claims, 3 Drawing Figures i 33 X- o mr l n fl n fl w n m 21 25 I l l23 29 35 1 1 37 a l 1 1 SUCCEEDlNGl 3/ I SWITCH 1 27 l l I l L 1 BISIELE I GWAL F i TO PRECEDING SWITCH PATENIEUHAR 61973 I 35: g. I

LTSATBLFSTGKAL TO PRECEDING swrr BRUSIILESS D.C. MOTOR USING MAGNETORESISTOR SENSING MEANS BACKGROUND OF THE INVENTION 1. FIELD OF THEINVENTION The invention relates to brushless d.c. motors and morespecifically to brushless d.c. motors using magnetic rotor positionsensing means.

2. Description of the Prior Art Brushless d.c. motors have found wideapplication in recent years. Various sensing means have been utilizedfor detecting rotor position in such motors. Photo-optical means, forinstance, are widely used for this purpose.

Photo-optical means, however, are not suitable for some hostileenvironments so that alternative means must be adopted.

Wound resolvers have also been used for rotor position sensing. Suchresolvers, however, are expensive so that their use is limited toapplications in which such complexity and expense can be tolerated.

Hall effect devices have also been used for rotor position sensing.Although these devices operate effectively, they require additionalcircuitry since they essentially essenially active devices.

SUMMARY OF THE INVENTION Stator windings of a brushless d.c. motor aredisposed around the periphery of the motor frame and energized throughindividual commutating switches in response to a rise in resistanceexperienced by associated magneto resistors when subjected to flux froma selected magnetic pole of the rotor. Closure of any switch generates adisabling signal that opens the previous switch in the desired sequence.The switches are rendered immune to the effect of the rise in resistanceof the individual magneto resistors when exposed to flux from thenon-selected magnetic pole of the rotor by positioning the resistors sothat this rise in resistance occurs while the associated switch isdisabled.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective drawingillustrating the physical arrangement of various elements of a motoremploying the invention;

FIG. 2 is a diagram useful in explaining the invention; and

FIG. 3 is a schematic diagram of a commutating switch that may be usedin practicing the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The brushless d.c. motor of thepresent invention uses commercially available magneto resistors forrotor position sensing. As presently preferred, such commerciallyavailable magneto resistors may be obtained in the form of a flatrectangular element that may conveniently be inserted between the frameof the brushless d.c. motor and the rotating permanently magnetizedrotor. As is well known in the art, magneto resistors are characterizedin that they exhibit a resistance that increases when the unit isexposed to magnetic flux. This phenomenon is used in the presentinvention by exposing the magneto resistors to a flux from thepermanently magnetized rotor of a brushless d.c. motor. As a magneticpole of the rotor approaches the magneto resistor during normalrotation, the resistance of the magneto resistor rises to a maximum peakand then decreases to a minimum value as the magnetic pole recedes. Themagneto resistors have proven to be useful in such applications sincethey are passive devices and require no auxiliary excitation apparatus.This is particularly useful in situations in which compactness,reliability and low cost are important. However, since a magnetoresistor when exposed to flux from a rotating permanent magnet rotorcannot distinguish between north and south magnetic poles, some meansmust be found to eliminate the effect of one of these poles.

FIG. 11 is an exploded perspective view illustrating the physicalconstruction of a motor employing the principles of the presentinvention. A diametrically magnetized rotor contains north and southpoles. The rotor is inserted inside the motor frame during fabricationwherein it is free to rotate in response to currents sequentiallyflowing in the three stator windings indicated. Three magneto resistorsare also mounted inside the motor frame in positions intermediateadjacent stator windings. These magneto resistors are sufficiently smallso that they may be inserted directly in the motor frame and stillprovide clearance for the rotor as it rotates.

FIG. 2 is a diagram useful in explaining the invention. As indicated,three commutating switches ll, 3 and 5 individually control the currentflowing through the three stator windings 7, 9 and 11, respectively. Thestator windings are spaced at equal intervals around the periphery ofthe motor frame. Three magneto resistors l3, l5 and 17 provide triggersignals which control the closing of the switches ll, 3 and 5,respectively. In the diagram of FIG. 2, counter-clockwise rotation ofthe rotor 19 is assumed. Thus it can be seen that a given magnetoresistor controls the closing of the next switch in the desired sequenceof rotation.

Each switch also contains means to disable the previous switch in thedesired sequence, as indicated in FIG. 2. Thus for example, magnetoresistor 13 provides a trigger pulse which closes the switch ll. Switch1, in turn, provides a disable signal when switch I is closed whichserves to open the preceding switch 5 and maintain this switch in theopen condition for an appropriate period of time.

FIG. 3 illustrates the circuits used in each of the commutatingswitches. The switch is energized from an appropriate d.c. source asindicated. The associated magneto resistor is connected in series with acalibrating resistor 21. The junction point between these two resistorsis connected to the base electrode of a preamplifier transistor 23. Thepreamplifier transistor 23 is connected to the voltage source throughappropriate collector and emitter resistors 25 and 27, respectively. Theemitter electrode of the preamplifier transistor 23 is also connected todrive transistors 29 and 31. The transistors 23, 29 and 31 cooperate toform an amplify- .ing means which serves to pass energizing currentthrough the associated stator winding 33 when the amplifying means isdriven into a conducting state, or to block the flow of energizingcurrent to the stator winding when the amplifying means is driven intothe cut-off or non-conducting state. A Zener diode 35 is com nectedacross the transistor 31 and its associated collector resistor toprotect this transistor from transients.

An auxiliary transistor 37 is also driven from the preamplifiertransistor 23. The auxiliary transistor 37 is driven into and out ofconduction simultaneously with the transistors 29 and 31. The transistor37 provides a disable signal that is applied to the preceding switch inthe motor.

The circuit of the switch further includes a disabling circuitcontaining a disabling circuit transistor 39, a series resistor 41, anda controlled rectifier 43. The controlled rectifier, which preferably isa silicon controlled rectifier, is connected to receive a disable signalfrom the succeeding switch in the sequence of operation.

When the associated magneto resistor experiences a rise in flux densitycaused by the approach of a magnetic pole, the resistance of the magnetoresistor increases thus raising the voltage level at the junction pointand eventually causing the preamplifier resistor 23 to conduct andthereby close the switch so as to energize the associated statorwinding.

However, if a disable signal is received from a succeeding switch, thissignal will fire the controlled rectifier 43 so as to effectively shortout the magneto resistor and clamp the base of the preamplifiertransistor 23 to ground level. After the disable signal terminates, thecontrolled rectifier will remain conductive until the magneto resistordecreases in resistance sufficiently to drop the voltage at the junctionpoint below the extinction voltage for the controlled rectifier.

The series resistor 41 is selected so that the extinction voltage at thejunction point occurs when the resistance of the associated magnetoresistor drops to a sufficiently low level in response to a suitable lowflux density. Similarly, the calibrating resistor 21 is selected so thatthe voltage at the junction point reaches a sufficiently high level todrive the amplifying means into conduction when the resistance of themagneto resistor increases due to a suitably high flux density.

The operation of the motor may be understood by referring to FIG. 2together with FIG. 3. Assume that the stator windings are each woundsoas to attract the north magnetic pole when the winding is energized.Assume further that the rotor is moving in a counterclockwise directionand is approaching the position wherein the north-south axis isvertical.

At this time, switch 1 will be closed so as to energize stator winding7. Furthermore, switch 1 will produce a disable signal that clamps thepreviously energized switch 5 in the open condition. During this time,any trigger signal from the magneto resistor 17 produced by theproximity of the south magnetic pole of the rotor cannot affect theswitch 5 since this switch is under control of the disable signal fromthe switch 1.

As the rotor rotation proceeds, magneto resistor is subjected toincreasing flux from the north pole of the magnetized rotor. This causesthe resistance of the magneto resistor 15 to increase accordingly. Thisincrease in resistance causes a corresponding increase in the voltage atthe junction point in the switch 3 and constitutes a trigger signal thateventually drives the amplifying means in the switch 3 into conduction.in a typical motor, the circuits of H6. 3 may be designed so thatswitching occurs when the junction voltage reaches about 2.1 volts andthe north pole is within about 60 of the corresponding magneto resistor.

When switch 3 closes, winding 9 is energized and acts to attract thenorth magnetic pole of the rotor so as to sustain rotation. Closure ofswitch 3 also drives the auxiliary transistor 37 in that switch intoconduction so as to produce a disabling signal which is applied to thecontrolled rectifier in the preceding switch 1.

This disabling signal fires the controlled rectifier in switch 1 so asto short out any junction voltage that may appear in the switch.Furthermore, at this time the associated magneto resistor 13 issubjected to a low flux density so that the junction voltage is low.These phenomena cooperate to turn off (open) switch 1 and therebyde-energize the stator winding 7.

At this time, magneto resistor 17 is exposed to high flux density fromthe south magnetic pole. However,

the signal from magneto resistor 17 maintains the controlled rectifierin the associated switch 5 in a conducting state so as to clamp thejunction voltage in switch 5 at a low level and maintain the amplifierin that switch in a cut-off condition.

In summary, the trigger signal occurring because of the proximity of thesouth magnetic pole to a magneto resistor is rendered ineffective whenthe south magnetic pole is approaching the magneto resistor by theaction of the disabling circuit. When the south magnetic pole is closeto the magneto resistor, but receding, the resultant trigger voltageacts only to sustain the clamping function initiated when the controlledrectifier was originally fired.

When the north magnetic pole subsequently reaches a position of about 30beyond the magneto resistor 15, the succeeding magneto resistor 17 isexposed to low magnetic flux. The resulting junction voltage in switch 5becomes too low to sustain the associated controlled rectifier in theconducting state and the controlled rectifier is extinguished.

As rotation continues to the point wherein the north magnetic pole isopposite the stator winding 9, the resistance of the succeeding magnetoresistor 17 is rising and that of the magneto resistor 15 is decreasing.Succeeding switch 5 closes shortly thereafter and opens switch 3.

The operation continues in this fashion so as to sustain rotation for aslong a period as desired.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

We claim:

1. A brushless d.c. motor of the type in which a permanent magnet rotorrotates in response to a rotating magnetic field established byindividual stator windings disposed around the inner periphery of themotor frame and wound so as to attract a selected magnetic pole of saidrotor,

said motor comprising individual switching means for energizing acorresponding stator winding in response to a trigger signal,

individual magneto resistors coupled to apply trigger signals to acorresponding switching means,

each of said magneto resistors being disposed around the inner peripheryof said motor frame in a position ahead of the associated stator windingso that a magneto resistor provides a trigger signal when the selectedmagnetic pole of the rotor approaches the associated stator winding,

means in each of said switching means for producing a disable signalwhen the switching means is closed,

means in each of said switching means for clamping the switch in theopen condition in response to a disable signal from an adjacentswitching means, said magneto resistors being further disposed so thatthe resistor is exposed to a maximum intensity of flux from thenon-selected magnetic pole of the rotor while the associated switchingmeans is clamped in the open condition.

2. The brushless d.c. rotor of claim 1 in which three stator windingsare disposed at equal intervals around the motor frame and a magnetoresistor is positioned midway between each pair of adjacent statorwindings,

each magneto resistor being coupled to provide trigger signals to theassociated switching means controlling the next adjacent stator windingin the direction of rotor rotation,

said associated switching means further being coupled to receive disablesignals from the switching means controlling the stator windingpositioned diametrically opposite the same magneto resistor.

3. The brushless d.c. motor of claim 2 wherein each switching meansincludes amplifying means for supplying energizing current to theassociated stator winding, voltage dividing means for driving saidamplifying means and a disabling circuit,

said voltage dividing means including a calibrating resistor and meansfor connecting the associated magneto resistor in series with saidcalibrating resistor so that the trigger signals from the associatedmagneto resistor appear at the junction of the calibrating resistor andthe magneto resistor,

said calibrating resistor being adjusted so that the amplifying means isdriven into conduction when the selected magnetic pole of the rotorreaches a specified angular displacement with respect to the associatedmagneto resistor. 4. The brushless d.c. motor of claim 3 wherein thespecified angular displacement in about 5. The brushless d.c. motor ofclaim 4 in which the disabling circuit includes a controlled rectifiercircuit connected across said voltage dividing means so as to short outthe associated magneto resistor when the controlled rectifier isconducting.

6. The brushless d.c. motor of claim 5 in which the controlled rectifiercircuit includes a series resistor,

a transistor, and a controlled rectifier in series relationship, saidcontrolled rectifier being effectively shunted across the magnetoresistor through said transistor,

said controlled rectifier being connected to respond to disable signalsfrom the succeeding switching means in the direction of rotor rotation.

7. The brushless d.c. motor of claim 6 wherein said transistor has abase electrode connected to the junction of said calibrating resistorand the associated magneto resistor, a collector electrode connectedthrough said series resistor to the opposite end of said calibratingresistor, and an emitter electrode connected to the anode of saidcontrolled rectifier,

said controlled rectifier further having a cathode connected to theopposite end of said magneto resistor whereby the conductioncharacteristics of said controlled rectifier are dependent upon saidcalibrating resistor and the voltage at said junction,

said calibrating resistor being selected so that the controlledrectifier is maintained in its conducting state until the voltage atsaid junction nears its maximum value.

8. The brushless d.c. motor of claim 7 wherein said amplifying meansfurther includes means to produce a disable signal when the amplifyingmeans is supplying energizing current to the associated stator winding.

1. A brushless d.c. motor of the type in which a permanent magnet rotorrotates in response to a rotating magnetic field established byindividual stator windings disposed around the inner periphery of themotor frame and wound so as to attract a selected magnetic pole of saidrotor, said motor comprising individual switching means for energizing acorresponding stator winding in response to a trigger signal, individualmagneto resistors coupled to apply trigger signals to a correspondingswitching means, each of said magneto resistors being disposed aroundthe inner periphery of said motor frame in a position ahead of theassociated stator winding so that a magneto resistor provides a triggersignal when the selected magnetic pole of the rotor approaches theassociated stator winding, means in each of said switching means forproducing a disable signal when the switching means is closed, means ineach of said switching means for clamping the switch in the opencondition in response to a disable signal from an adjacent switchingmeans, said magneto resistors being further disposed so that theresistor is exposed to a maximum intensity of flux from the non-selectedmagnetic pole of the rotor while the associated switching means isclamped in the open condition.
 1. A brushless d.c. motor of the type inwhich a permanent magnet rotor rotates in response to a rotatingmagnetic field established by individual stator windings disposed aroundthe inner periphery of the motor frame and wound so as to attract aselected magnetic pole of said rotor, said motor comprising individualswitching means for energizing a corresponding stator winding inresponse to a trigger signal, individual magneto resistors coupled toapply trigger signals to a corresponding switching means, each of saidmagneto resistors being disposed around the inner periphery of saidmotor frame in a position ahead of the associated stator winding so thata magneto resistor provides a trigger signal when the selected magneticpole of the rotor approaches the associated stator winding, means ineach of said switching means for producing a disable signal when theswitching means is closed, means in each of said switching means forclamping the switch in the open condition in response to a disablesignal from an adjacent switching means, said magneto resistors beingfurther disposed so that the resistor is exposed to a maximum intensityof flux from the non-selected magnetic pole of the rotor while theassociated switching means is clamped in the open condition.
 2. Thebrushless d.c. rotor of claim 1 in which three stator windings aredisposed at equal intervals around the motor frame and a magnetoresistor is positioned midway between each pair of adjacent statorwindings, each magneto resistor being coupled to provide trigger signalsto the associated switching means controlling the next adjacent statorwinding in the direction of rotor rotation, said associated switchingmeans further being coupled to receive disable signals from theswitching means controlling the stator winding positioned diametricallyopposite the same magneto resistor.
 3. The brushless d.c. motor of claim2 wherein each switching means includes amplifying means for supplyingenergizing current to the associated stator winding, voltage dividingmeans for driving said amplifying means and a disabling circuit, saidvoltage dividing means including a calibrating resistor and means forconnecting the associated magneto resistor in series with saidcalibrating resistor so that the trigger signals from the associatedmagneto resistor appear at the junction of the calibrating resistor andthe magneto resistor, said calibrating resistor being adjusted so thatthe amplifying means is driven into conduction when the selectedmagnetic pole of the rotor reaches a specified angular displacement withrespect to the associated magneto resistor.
 4. The brushless d.c. motorof claim 3 wherein the specified angular displacement in about 60*. 5.The brushless d.c. motor of claim 4 in which the disabling circuitincludes a controlled rectifier circuit connected across said voltagedividing means so as to short out the associated magneto resistor whenthe controlled rectifier is conducting.
 6. The brushless d.c. motor ofclaim 5 in which the controlled rectifier circuit includes a seriesresistor, a transistor, and a controlled rectifier in seriesrelationship, said controlled rectifier being effectively shunted acrossthe magneto resistor through said transistor, said controlled rectifierbeing connected to respond to disable signals from the succeedingswitching means in the direction of rotor rotation.
 7. The brushlessd.c. motor of claim 6 wherein said transistor has a base electrodeconnected to the junction of said calibrating resistor and theassociated magneto resistor, a collector electrode connected throughsaid series resistor to the opposite end of said calibrating resistor,and an emitter electrode connected to the anode of said controlledrectifier, said controlled rectifier further having a cathode connectedto the opposite end of said magneto resistor whereby the conductioncharacteristics of said controlled rectifier are dependent upon saidcalibrating resistor and the voltage at said junction, said calibratingresistor being selected so that the controlled rectifier is maintainedin its conducting state until the voltage at said junction nears itsmaximum value.